Dipsticks are commonly incorporated with internal combustion engines to provide a visual check as to the level of oil in the engine crankcase. A typical dipstick is a flat rod that extends down through a tube into the crankcase or other oil reservoir and the upper end of the dipstick carries a cap which is secured to the upper portion of the tube and supports the dipstick within the tube. On certain engines, particularly single cylinder engines, the dipstick extends down into the crankcase through the oil fill tube, and is secured to the cap that encloses the upper end of the oil fill tube.
With small engines such as used with lawnmowers and the like, it is important that the cap be sealed to the upper end of the oil fill tube to prevent leakage of oil from the tube in the event the engine is tilted during usage. In some instances, the cap is threaded to the upper end of the fill tube, but the threaded connection is not feasible where the fill tube is bent to follow the configuration of a non-linear fill tube.
U.S. Pat. No. 3,474,884 assigned to a common assignee with the present application, shows an oil fill tube assembly in which the cap which carries the dipstick is secured to the upper end of the tube by flexible prongs which extend downwardly from the undersurface of the cap and engage ledges on the inner surface of the fill tube. However, the construction shown on the aforementioned patent does not provide a positive type seal and the cap is not oriented with the fill tube and engine, meaning that any logo or instructions on the cap are not necessarily assembled in the same relation to the fill tube at all times.